Tianeptine oxalate salts and polymorphs

ABSTRACT

Disclosed herein is an oxalate salt/co-crystal (tianeptine oxalate) of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f] [1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide (tianeptine) as shown in Formula I:

FIELD OF THE INVENTION

The present disclosure is in the field of salts/co-crystals of tianeptine, including polymorphic forms of tianeptine oxalate, methods of making the salts and polymorphic forms, and pharmaceutical compositions comprising them are also described.

RELATED APPLICATIONS

This application claims the benefit of and priority from U.S. Provisional Application 62/439,533, filed Dec. 28, 2016, the contents and disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE DISCLOSURE

Tianeptine, or 7-[(3-chloro-6-methyl-5,5-dioxo-11H-benzo[c][2,1]benzothiazepin-11-yl)amino]heptanoic acid, is an antidepressant with cognitive restorative effects. Investigators have reported that it can be used to treat post-traumatic stress disorder (PTSD) (Onder E. et al., (2005), European Psychiatry 21:174-179).

Although tianeptine shares structural similarities to classic tricyclic antidepressants, its pharmacological behavior is unique. More commonly known by the commercial names Stablon®, Coaxil, Tatinol, Tianeurax, and Salymbra, tianeptine is currently available throughout Europe, Asia, and Latin America for the treatment of depression. Tianeptine modulates the glutamatergic system and reverses the inhibitory neuroplasticity observed during periods of stress and steroid use. In modulating the glutamatergic system, tianeptine normalizes glutamate levels in the hippocampus, amygdala, and prefrontal cortex. Through genomic and non-genomic mechanisms, glutamate modulation restores plasticity, relieves inhibition of long-term potentiation, and reverses structural changes induced by chronic exposure to corticosteroids.

Tianeptine's anxiolytic properties and its reported ability to modulate the neuroendocrine stress response suggest that it can be used to treat PTSD. In fact, several studies have shown tianeptine to be an effective therapy for patients with PTSD because it is reported to improve many of the condition's characteristic symptoms (Crocq L & Gouj on C: The Anxio-Depressive component of the psychotraumatic syndrome and its treatment by tianeptine. Psychol Med, 1994; 26 (2): 192-214; Rumyantseva G M & Stepanov A L: Post-traumatic stress disorder in different types of stress (clinical features and treatment). Neurosci Behav Physiol, 2008; 38:55-61; and Frančišković, Tanja, et al. “Tianeptine in the combined treatment of combat related posttraumatic stress disorder.” Psychiatria Danubina 23(3) (2011): 257-263).

In addition to tianeptine's neuro-protective actions, including its ability to reverse the structural changes and inhibition of long term potentiation (LTP) caused by steroid exposure, it is reported to be potentially useful for treating neurocognitive dysfunction and similar side effects in patients treated with corticosteroids. Tianeptine's ability to restore cognitive functionality has also been observed in some animal models.

Due to their anti-inflammatory properties, corticosteroids are used in the treatment of many diseases and conditions including asthma, systematic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, nephritic syndrome, cancer, organ transplantation, autoimmune hepatitis, hypersensitivity reactions, cardiogenic and septic shock, glucocorticoid deficiency diseases (Addison's disease and panhypopituitarism), and multiple sclerosis. When the body experiences stress, the adrenal glands release corticosteroids, such as cortisol. Synthetic corticosteroids work by mimicking steroid hormones naturally produced by the adrenal glands. Upon release into the body's circulatory system, these hormones help to regulate inflammation as well as the body's immune response. Common synthetic corticosteroids include prednisone, cortisone, hydrocortisone, and methylprednisone. Supplementing the body's normal hormone levels with synthetic corticosteroids induces a genomic cascade that reduces inflammation and suppresses the immune response. This genomic cascade is initiated by the binding of steroids to intracellular glucocorticoid receptors (GRs) (Datson, N A et al. Identification of corticosteroid-responsive genes in rat hippocampus using serial analysis of gene expression. European Journal of Neuroscience. 2001; 14(4): 675-689).

Despite their widespread use and therapeutic benefit, synthetic corticosteroids often cause numerous adverse psychological, metabolic, and somatic side effects (Warrington T P, Bostwick J M. Psychiatric adverse effects of corticosteroids. Mayo Clinic Proceedings. 2006; 81(10)). Examples of such somatic side effects are displayed in Table 1. Psychological side effects include mood and anxiety disorders, behavioral disturbance, cognitive impairment, and psychosis.

TABLE 1 Somatic Side Effects of Corticosteroid Use Cardiovascular Hypertension Accelerated atherosclerosis Dermatologic Acne Alopecia Hirsutism Striae Skin atrophy Purpura Endocrine/Metabolic Obesity Diabetes Mellitus Adrenal-pituitary axis suppression Hyperlipidemia Fluid and sodium retention Loss of potassium, calcium, and nitrogen Delayed growth Neurologic Pseudotumor cerebri Gastrointestinal Peptic ulcer disease Pancreatitis Fatty liver Hematologic Leukocytosis Neutrophilia Lymphophenia Infectious Oral candidiasis Increased risk of systemic infection Musculoskeletal Myopathy Osteoporosis Avascular necrosis Ophthalmologic Cataracts Glaucoma

Cognitive impairment, anxiety and mood disorders are among the most common psychological side effects of corticosteroid use. Especially for patients who require long-term steroid treatment, these effects result in a diminished quality of life. For example, 33% of individuals taking corticosteroids (about 13 million) are reported to exhibit deficits in working or short-term memory, declarative memory, attention span and concentration (academic & occupational performance), and executive functioning (Stoudemire A, Anfinson T, Edwards J. Corticosteroid-induced delirium and dependency. Gen Hosp Psychiatry. 1984; 141: 369-372). In extreme cases, steroids can even induce delirium, dementia (persistent memory impairment), and mania (Varney N R, Alexander B, Maclndoe J H. Reversible steroid dementia in patients without steroid psychosis. Am J Psychiatry. 1984; 141:369-372).

Currently, there is no FDA approved drug designated for the treatment of the cognitive impairment and similar psychiatric disorders, such as anxiety and mood disorders, associated with corticosteroid use. Tricyclic antidepressants do not appear to be useful therapeutic agents to modulate the psychiatric side effects induced by steroids, and may actually exacerbate these symptoms (Lewis D A, Smith R E. Steroid-induced Psychiatric Syndromes: A Report of 14 Cases and a review of the Literature. Journal of Affective Disorders. 1983; 5: 319-332). In addition, there are no alternatives to corticosteroids for the treatment of inflammatory disorders—corticosteroids must be used.

The disclosure herein relates to more stable chemical formulations, crystalline salts and polymorphs thereof of tianeptine for use in the treatment of neurocognitive dysfunction and related psychiatric disorders induced by corticosteroid treatment. These disorders include trauma- and stressor-related disorders including PTSD and acute stress disorder; depressive disorders including major depressive disorder, persistent depressive disorder, bipolar depression, and premenstrual dysphoric disorder; neurodegenerative diseases such as Alzheimer's disease and multi-infarct dementia; and neurodevelopmental disorders including attention-deficit\hyperactivity disorder. The present disclosure can also be used in the treatment of asthma and chronic obstructive pulmonary disorder.

SUMMARY OF THE INVENTION

In some aspects, the disclosure herein comprises an oxalate salt/co-crystal (tianeptine oxalate) of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f][1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide (tianeptine) as shown in Formula I, including crystalline and polymorph forms:

The tianeptine hemi-oxalate salt is shown as Formula (II):

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Overlayed XRPD patterns of tianeptine hemi-oxalate Form A, tianeptine free base and oxalic acid.

FIG. 2: XRPD pattern of tianeptine hemi-oxalate Form A.

FIG. 3: DSC profile of tianeptine hemi-oxalate Form A.

FIG. 4: TGA profile of tianeptine hemi-oxalate Form A.

FIG. 5: FTIR spectrum of tianeptine hemi-oxalate Form A.

FIG. 6: 1H NMR spectrum (in DMSO-d₆) of tianeptine hemi-oxalate Form A.

FIG. 7: Ortep drawing of the asymmetric unit with elipsoids of tianeptine hemi-oxalate (dianion).

FIG. 8: Hydrogen bonds between the oxalate (central) and the four molecules of tianeptine.

FIG. 9: XRPD comparison between tianeptine free base, tianeptine hemi-oxalate Form A, and tianeptine hemi-oxalate Form A+tianeptine mono-oxalate Form A.

FIG. 10: XRPD pattern of tianeptine mono-oxalate Form A.

FIG. 11: FT-IR spectrum for tianeptine mono-oxalate Form A.

FIG. 12: DSC profile of tianeptine mono-oxalate Form A.

FIG. 13: TGA profile of tianeptine mono-oxalate Form A.

FIG. 14: XRPD pattern of tianeptine mono-oxalate Form B.

FIG. 15: FT-IR spectrum of tianeptine mono-oxalate Form B.

FIG. 16: DSC profile of tianeptine mono-oxalate Form B.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present disclosure relates to salt/co-crystal forms of tianeptine oxalate, more particularly tianeptine hemi-oxalate and/or tianeptine mono-oxalate. The properties of the salts/co-crystals of tianeptine are improved relative to one or more known forms of tianeptine, such as tianeptine free base or tianeptine sodium (the currently available form of tianeptine). The salts/co-crystals can take several forms including, but not limited to, hydrates and solvates as well as various stoichiometric ratios of tianeptine to oxalic acid. The disclosure also includes other forms of tianeptine oxalate including, but not limited to, polymorphs and amorphous forms. The disclosure also provides pharmaceutical compositions comprising the salts/co-crystals of tianeptine oxalate, methods of making those salts/co-crystals, and related methods of treatment.

One embodiment of this disclosure is an oxalate salt/co-crystal (tianeptine oxalate).

In some embodiments, the tianeptine oxalate is crystalline.

In some embodiments, the salt/co-crystal is crystalline tianeptine hemi-oxalate Form A, tianeptine mono-oxalate Form A, tianeptine mono-oxalate Form B, or mixtures thereof.

In some embodiments, the salt/co-crystal is anhydrous crystalline tianeptine hemi-oxalate Form A, tianeptine mono-oxalate Form A, tianeptine mono-oxalate Form B, or combinations thereof.

A pharmaceutical composition comprising the salt/co-crystal of tianeptine oxalate and a pharmaceutically acceptable carrier, diluent or excipient.

In some embodiments, the salt/co-crystal of the pharmaceutical composition is anhydrous crystalline tianeptine hemi-oxalate Form A, mono-oxalate Form A, or a combination thereof.

In some embodiments, the salt/co-crystal of the pharmaceutical composition is tianeptine hemi-oxalate Form A.

In some embodiments, the anhydrous crystalline tianeptine hemi-oxalate Form A exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak at about 8.2, 8.6, 9.1, and 9.5 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine hemi-oxalate Form A exhibits an XRPD pattern comprising at least one peak at about 8.2, 8.6, 9.1, and 9.5 degrees 2θ with an associated tolerance of 0.3 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine hemi-oxalate Form A exhibits an XRPD pattern further comprising at least one peak selected from the group consisting of about 4.5, 8.2, 8.6, 9.1, 9.5, 11.5, 14.2, 15.2, 15.8, 16.4, 19.2, 22.1, 23.9, 26.9, and 27.4 degrees 2θ.

In some embodiments, the anhydrous tianeptine hemi-oxalate crystalline Form A exhibits an XRPD pattern substantially the same as FIG. 2.

In some embodiments, the anhydrous crystalline tianeptine hemi-oxalate Form A is characterized by at least one of a) an XRPD pattern exhibiting at least four of the peaks shown in FIG. 2; b) an FT-IR spectrum substantially the same as FIG. 5; and c) an NMR spectrum substantially the same as FIG. 6.

In some embodiments, the crystalline form is a tianeptine mono-oxalate Form A.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form A exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak at about 10.2 and 10.5 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form A exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak at about 10.2 and 10.5 degrees 2θ with an associated tolerance of 0.3 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form A exhibits an XRPD pattern further comprising at least one peak selected from the group consisting of about 7.5, 8.3, 10.2, 10.5, 11.9, 14.7, 16.2, 16.3, 17.9, 18.7, 21.0, 21.7, and 22.1 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form A exhibits an XRPD pattern substantially the same as FIG. 10.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form A is characterized by at least one of a) an XRPD pattern exhibiting at least four of the peaks shown in FIG. 10; and b) an FT-IR spectrum substantially the same as FIG. 11.

In some embodiments, the crystalline form is a tianeptine mono-oxalate Form B.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form B exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak at about 10.4 and 10.8 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form B exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak at about 10.4 and 10.8 degrees 2θ with an associated tolerance of 0.3 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form B exhibits an XRPD pattern further comprising at least one peak selected from the group consisting of about 7.4, 7.8, 10.4, 10.8, 13.7, 14.8, 15.6, 16, 17.5, 19.9, 21.0, 20.2, 20.4, 20.9, 21.3, 21.6 and 21.9 degrees 2θ.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form B exhibits an XRPD pattern substantially the same as FIG. 14.

In some embodiments, the anhydrous crystalline tianeptine mono-oxalate Form B is characterized by at least one of a) an XRPD pattern exhibiting at least four of the peaks shown in FIG. 14; and b) an FT-IR spectrum substantially the same as FIG. 15.

In some embodiments, the pharmaceutical composition is in a solid form, a liquid form, a suspension form, a sustained release form, a delayed release form, or an extended release form.

In some embodiments, the anhydrous tianeptine oxalate crystalline form comprises a mixture of tianeptine hemi-oxalate Form A and tianeptine mono-oxalate Form A.

In some embodiments, the anhydrous tianeptine oxalate crystalline form comprises a mixture of tianeptine hemi-oxalate Form A and tianeptine mono-oxalate Form A, wherein the anhydrous tianeptine oxalate crystalline form exhibits an XRPD pattern comprising at least one peak selected from the group consisting of about 10.2 and 10.5 degrees 2θ.

In some embodiments, the anhydrous tianeptine oxalate crystalline form comprises a mixture of tianeptine hemi-oxalate Form A and tianeptine mono-oxalate Form A, wherein the anhydrous tianeptine oxalate crystalline form exhibits an XRPD pattern comprising at least one peak selected from the group consisting of about 10.2 and 10.5 degrees 2θ with an associated tolerance of 0.3 degrees 2θ.

In some embodiments, the anhydrous tianeptine oxalate crystalline form comprises a mixture of tianeptine hemi-oxalate Form A and tianeptine mono-oxalate Form A, wherein the crystalline form exhibits an XRPD pattern further comprising at least one peak selected from the group consisting of about 7.5, 8.3, 10.2, 10.5, 11.9, 14.7, 16.2, 16.3, 17.9, 18.7, 21.0, 21.7, and 22.1 degrees 2θ.

In some embodiments, the anhydrous tianeptine oxalate crystalline form comprises a mixture of tianeptine hemi-oxalate Form A and tianeptine mono-oxalate Form A, wherein the crystalline form exhibits an XRPD pattern substantially the same as FIG. 9.

The salt/co-crystal forms of the various embodiments of this disclosure provide improved stability, bioavailability, lower hygroscopicity, more consistent pK, and easier processing and manufacturing, including pharmaceutical compositions as compared to sodium tianeptine.

In one aspect, this disclosure also provides formulations of tianeptine oxalate salts to be developed as first generation therapy for the treatment of corticosteroid-induced psychological side effects.

The tianeptine oxalate in the salt/co-crystal forms of the various embodiments of the disclosure has a higher melting point than the formulation of tianeptine (Stablon®) currently used to treat depression, suggesting greater crystalline stability and thus improved product performance in tablet form. As such, tianeptine oxalate has easier tablet formation as compared to Stablon® and improved tolerability such as fewer adverse events and severe adverse events.

In some embodiments of this disclosure, the tianeptine hemi-oxalate (Form A) and/or mono-oxalate (Form A and/or Form B) salts can be incorporated into a pharmaceutical composition. In some embodiments, the composition is in any one the following forms: sustained release, controlled release, delayed release or extended release. In some embodiments, the tianeptine hemi-oxalate and/or mono-oxalate mixtures can be incorporated into a hydrophilic matrix system with a polymer. The tianeptine hemi-oxalate and/or mono-oxalate mixtures are released by dissolution, diffusion and/or erosion from the hydrophilic matrix when the polymer swells on contact with the aqueous medium to form a gel layer on the surface of the system.

In another embodiment, the tianeptine hemi-oxalate (Form A) and/or mono-oxalate (Form A and/or Form B) can be incorporated into a pharmaceutical composition comprising two or more layers of tianeptine hemi-oxalate and/or oxalate such that one layer is substantially released prior to the substantial release of another layer in vivo. In another embodiment, the hemi-oxalate and/or oxalate salt of tianeptine can be incorporated into a pharmaceutical composition comprising pellets, wherein the pellets have varying extents or compositions of coating so as to enable release of tianeptine over a substantially longer period of time than that of the currently available tianeptine (e.g., STABLON®, Coaxil, or Tatinol).

In another embodiment, the hemi-oxalate (Form A) and/or mono-oxalate (Form A and/or Form B) salt of tianeptine can be incorporated into an osmotically active pharmaceutical composition suitable for oral administration. Osmotically active pharmaceutical compositions, osmotic pumps, osmotic drug delivery, and other osmotic technology suitable for oral administration can include, but are not limited to, OROS® Push-Pull and OROS® Tri-layer pharmaceutical compositions. In another embodiment, the tianeptine hemi-oxalate (Form A) and/or mono-oxalate (Form A and/or Form B) salt of tianeptine can be incorporated into an OROS® drug delivery system. Such controlled release pharmaceutical compositions comprising the oxalate salt of tianeptine, such as an osmotically active pharmaceutical composition suitable for oral administration, may lead to a longer lasting therapeutic effect than that of tianeptine sodium salt in the currently marketed form.

In some embodiments, the compositions of this disclosure may be in solid dosage forms such as capsules, tablets, dragrees, pills, lozenges, powders and granule. Where appropriate, they may be prepared with coatings such as enteric coatings or they may be formulated so as to provide controlled releases of one or more active ingredient such as sustained or prolonged release according to methods well known in the art. In certain embodiments, the composition is in form of a slow, controlled, or extended release. The term “extended release” is widely recognized in the art of pharmaceutical sciences and is used herein to refer to a controlled release of an active compound or agent from a dosage form to an environment over (throughout or during) an extended period of time, e.g. greater than or equal to one hour. An extended release dosage form will release drug at substantially constant rate over an extended period of time or a substantially constant amount of drug will be released incrementally over an extended period of time. The term “extended release” used herein includes the terms “controlled release”, “prolonged release”, “sustained release”, or “slow release”, as these terms are used in the pharmaceutical sciences. The composition may also be in liquid dosage forms including solutions, emulsions, suspensions, syrups, and elixirs. The composition may be formulated for once daily administration.

Instrumental Techniques

Instrumental Techniques

Identification of the crystalline forms obtained by the present invention can be made by methods known in the art, including but not limited to X-Ray powder diffraction (XRPD), Fourier Transform Infrared (FT-IR) spectra, Differential Scanning calorimetry (DSC), Thermogravimetric Analysis (TGA), and Nuclear Magnetic Resonance (NMR). Furthermore, it should be understood that operator, instrument and other related changes may result in some margin of error with respect to analytical characterization of the salts/co-crystals.

Differential Scanning Calorimetry:

The analysis was carried out on the untreated sample using a DSC Mettler Toledo DSC1. The sample was weighed in an aluminum pan hermetically sealed with an aluminum cover. The analysis was performed by heating the sample from 25° C. to 350° C. at 10K/min.

TABLE 2 Technical Specification Temperature range −170° C . . . 600° C. Heating rates 0.001 K/min . . . 100 K/min Cooling rate 0.001 K/min . . . 100 K/min (depending on temperature) Sensor Heat flux system Measurement range 0 mW . . . ±600 mW Temperature accuracy 0.1 K Enthalpy accuracy Generally <1% Cooling options Forced air (down to RT), LN2 (down to −170° C.) Purge gas rate 60 mL/min Intracooler for the extended −40° C . . . 600° C. rate Thermogravimetric Analysis:

The TG analysis was carried out on an untreated sample using the Mettler Toledo TGA/DSC1. The sample was weighed in an aluminum pan hermetically sealed with an aluminum pierced cover. The analysis was performed by heating the sample from 25° C. to 450° C. at 10K/min.

TABLE 3 Temperature Data Temperature range RT . . . 1100° C. Temperature accuracy ±1 K Temperature precision ±0.4 K Heating rate 0.02 . . . 250 K/min Cooling time 20 min (1100° C . . . 100° C.) Sample volume ≤100 μL

TABLE 4 Special modes Automation 34 sample positions TGA-FTIR Coupled with Thermo Nicolet iS10 spectrometer Balance data XP5 Measurement range ≤5 g Resolution 1.0 μg Weighing accuracy  0.005% Weighing precision 0.0025% Internal ring weights 2 Blank curve Better than ±10 μg over the whole temperature range reproducibility X-Ray Powder Diffraction (XRPD):

X-ray powder diffraction patterns were obtained using an X'Pert PRO PANalytical X-ray Diffractometer.

The X'Pert PRO PANalytical X-ray Diffractometer was equipped with a copper source (Cu/K_(α)1.5406 Å). Diffractogram was acquired using control software (X'Pert Data Collector vs. 2.2d) under ambient conditions at a power setting of 40 kV at 40 mA in reflection mode, while spinning over 360 degrees at 1 degree/second.

TABLE 5 (X-Ray Powder Diffraction (XRPD): Measurement Details) Measurement type: Single scan Sample mode: Reflection Scan Scan axis: Gonio Scan range (°): 3.0010-39.9997 Step size (°): 0.0167 Counting time (s): 12.700 No. of points: 2214 Scan mode: Continuous Used wavelength Intended wavelength type: Kα1 Kα1 (A): 1.540598 Kα2 (A): 1.544426 Kα2/Kα1 intensity ratio: 0.50 Kα (A): 1.541874 Kβ (A): 1.392250 Incident beam path Radius (mm): 240.0

TABLE 6 (X-Ray Powder Diffraction (XRPD): X-Ray Tube) Name: PW3373/00 Cu LFF DK184511 Anode material: Cu Voltage (kV): 40    Current (mA): 40    Focus Focus type: Line Length (mm): 12.0  width (mm): 0.4  Take-off angle (°): 6.0  Soller slit Name: Soller 0.04 rad. Opening (rad.): 0.04 Mask Name: Inc. Mask Fixed 15 mm (MPD/MRD) Width (mm): 11.60  Anti-scatter slit Name: Slit Fixed ½° Type: Fixed Height (mm): 0.76 Divergence slit Name: Slit Fixed ¼° Type: Fixed Height (mm): 0.76 Sample movement Movement type: Spinning Rotation time (s): 1.0  Diffracted beam path Radius (mm): 240.0   Anti-scatter slit Name: Anti-Scatter Slit 5.0 mm Type: Fixed Height (mm): 5.00 Soller slit Name: Soller 0.04 rad. Opening (rad.): 0.04 Filter Name: Nickel Thickness (mm):  0.020 Material: Ni

TABLE 7 (X-Ray Powder Diffraction (XRPD): Detector) Name: X'Celerator Type: RTMS detector PHD - Lower level (%): 39.5 PHD - Upper level (%): 80.0 Mode: Scanning Active length (°):   2.122 Fourier Transform Infrared Spectroscopy (FT-IR):

The analysis was carried out on an untreated sample using a Thermo Nicolet iS50—ATR module Spectrometer equipped with a Smart Performer Diamond, DTGS KBr Detector, IR Source, and KBr Beam splitter. The sample was measured using the parameters described the Table 8 below.

TABLE 8 Experimental Conditions Resolution 4000-650 cm−1 Number of sample scans 32 Number of background scans 32 Sample gain 8 Optical Velocity 0.6329 Aperture 100.00 Nuclear Magnetic Resonance (NMR):

The 1H NMR spectra were acquired at ambient temperature on a Gemini Varian 400 MHz spectrometer. Samples were prepared for NMR spectroscopy as ˜5-50 mg solutions in DMSO-d6. For each sample 16 transients with a delay of t1=1 sec were collected at 25° C.

Crystal Structure Data:

All crystal data were collected on an Oxford Xcalibur S instrument using Mo Kα radiation (λ=0.71073 Å) and a graphite monochromator at room temperature. SHELX97 was used for structure solution and refinement and was based on F2. Non-hydrogen atoms were refined anisotropically. Hydrogen atoms bound to carbon and nitrogen atoms were added in calculated positions. Hydroxyl hydrogen atoms were located using a Fourier map and their position refined. The program mercury was used for figure and calculation of X-ray powder patterns on the basis of single-crystal data.

Definitions

For the purposes of this specification and appended claims, unless otherwise indicated, all numbers expressing quantities, percentages or proportions, and other numerical values used in the specification and claims, are to be understood as being modified in all instances by the term “about.” As used herein, the meaning of the term “about” depends upon the context in which it is used. When used with respect to the position of a peak on an X-ray powder diffraction (XRPD) pattern, the term “about” includes peaks within an associated tolerance of ±0.3 degrees 2θ. For example, as used herein, an XRPD peak at “about 10.0 degrees 2θ” means that the stated peak occurs from 9.7 to 10.3 degrees 2θ. When used with respect to the position of a peak on a solid state 13C NMR spectrum, the term “about” includes peaks within ±0.2 ppm of the stated position. For example, as used herein, a 13C NMR spectrum peak at “about 100.0 ppm” means that the stated peak occurs from 99.8 to 100.2 ppm. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained.

As used herein, the term “substantially” in reference to an XRPD pattern refers to a spectrum having at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 peaks (perhaps differing in amplitude) in common with the referenced pattern; or a pattern having a tolerance of ±0.3 degrees 2θ within the referenced peaks. In reference to an NMR pattern, “substantially” refers to a spectrum having at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 peaks (perhaps differing in amplitude) in common with the referenced pattern; or a pattern having a tolerance of ±0.2 ppm within the referenced peaks. In reference to an FT-IR pattern, “substantially” refers to a spectrum having at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15 peaks (perhaps differing in amplitude) in common with the referenced pattern; or a pattern having a tolerance of ±0.5 cm⁻¹ within the referenced peaks.

As used herein, the term “co-crystal” refers to a molecular adduct of two molecules, each of which is solid at room temperature. A tianeptine oxalate co-crystal is a molecular adduct of tianeptine and any one of oxalate, hemi-oxalate, and mono-oxalate. The two molecules of the adduct form hydrogen bonds without transferring hydrogen between the molecules.

As used in this specification and the appended claims, the singular forms “a,” “an,” and “the,” include plural references unless expressly and unequivocally limited to one referent.

As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

As used herein, the term “comprising” means including elements or steps that are identified following that term, but any such elements or steps are not exhaustive, and an embodiment can include other elements or steps.

As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.

Example 1 Tianeptine Hemi-Oxalate Form A

100-1000 mg of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f][1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide—the starting material (SM) and 20-200 mg of oxalic acid (1 eq.) were mixed in acetone (2-20 mL) and the solution was heated at 40-60° C. until total dissolution occurred. The clear solution was cooled at room temperature and stirred for 12-24 hours. The white precipitate was recovered under vacuum, washed with acetone and dried at 40-60° C. for 12-24 hours.

TABLE 9 Characterization details of Tianeptine Hemi-Oxalate Form A Techniques/ experiment Results for Tianeptine Hemi Oxalate Form A Synthesis Tianeptine hemi oxalate Form A was prepared by precipitation from an acetone solution of tianeptine and oxalic acid XRPD The evidenced crystalline form was labeled as Form A FT-IR The infrared spectrum confirmed the formation of a new species DSC The DSC profile showed an endothermic peak at approximately 205° C. (Onset 204.43° C.). TGA The TGA profile was typical of an anhydrous compound decomposing above 200° C. EGA showed the evolution of CO₂ confirming the presence of the coformer 1H-NMR 1H-NMR confirmed the structural integrity of the tianeptine whereas the coformer was not visible. The protons of the molecule underwent slight shifts in their resonance frequencies DSC/TGA

The DSC profile of tianeptine hemi-oxalate Form A as illustrated in FIG. 3 was characterized by an endothermic event which took place just before sample decomposition. The peak at 205° C. (Onset 204.43° C.) was due to the sample melting and the broad shoulder was associated with decomposition.

The TGA profile of tianeptine hemi-oxalate Form A as illustrated in FIG. 4 is typical of an anhydrous compound. Sample decomposition was characterized by the first weight loss of 8.13% w/w, which corresponded to 0.5 equivalents of oxalic acid. A stoichiometry of 1:0.5 between tianeptine:oxalic acid was suggested. The oxalate showed a very high melting point above the 200° C., when the melting and decomposition occurred at the same time.

XRPD

FIGS. 1 and 2 illustrate the XRPD pattern of the tianeptine hemi-oxalate salt.

TABLE 10 XRPD peaks list of Tianeptine hemi-oxalate Form A Pos. Height FWHM d-spacing Rel. Int. [°2Th.] [cts] [°2Th.] [Å] [%] 4.5010 34.97 0.9368 19.63245 1.56 8.2252 607.21 0.0669 10.74980 27.02 8.6666 1323.95 0.1004 10.20325 58.92 9.1460 799.69 0.0836 9.66947 35.59 9.5853 1166.90 0.1004 9.22727 51.93 11.5807 1467.88 0.1004 7.64149 65.33 14.1914 714.49 0.1004 6.24106 31.80 15.2018 454.39 0.0836 5.82843 20.22 15.7987 1647.80 0.1338 5.60952 73.33 16.4473 422.17 0.1004 5.38976 18.79 19.1657 2246.97 0.1506 4.63098 100.00 22.0891 773.13 0.0836 4.02427 34.41 23.9294 1253.33 0.1840 3.71878 55.78 26.8794 476.25 0.1673 3.31697 21.20 27.4168 751.73 0.1338 3.25317 33.46 28.3866 229.43 0.1171 3.14419 10.21 28.7606 152.29 0.1673 3.10416 6.78 29.1253 224.40 0.1171 3.06611 9.99 29.8763 174.82 0.1673 2.99072 7.78 30.6136 287.62 0.1171 2.92035 12.80 31.5515 44.50 0.1171 2.83565 1.98 32.1254 89.62 0.2676 2.78629 3.99 33.5303 64.44 0.1673 2.67270 2.87 34.4758 64.22 0.1338 2.60153 2.86 34.9300 96.39 0.1673 2.56873 4.29 35.4906 138.82 0.2007 2.52944 6.18 36.0079 82.53 0.1004 2.49428 3.67 36.4741 23.82 0.1004 2.46346 1.06 36.9223 65.21 0.1004 2.43458 2.90 37.8937 29.49 0.4684 2.37437 1.31 39.6005 74.60 0.2676 2.27588 3.32

The FT-IR spectrum and peaks of tianeptine hemi-oxalate Form A are illustrated in FIG. 5 and Table 11. Comparison with the starting material showed many differences including the disappearance of the NH stretching at 3300 cm⁻¹ and the appearance of the broad band at 1615 cm⁻¹ from the C═O stretching ascribable to the presence of the oxalate.

TABLE 11 FT-IR Peak List of Tianeptine hemi-Oxalate Form A Position (cm−1) Intensity [% T] 432.49 62.178 466.63 50.071 488.10 54.917 519.00 60.449 539.59 38.578 570.25 27.820 584.10 25.441 602.02 50.697 633.03 83.567 670.00 56.310 692.71 61.686 724.21 47.215 765.61 28.950 814.36 71.754 847.32 51.291 876.39 70.707 900.03 63.088 911.81 64.771 958.77 81.157 1042.00 54.177 1055.28 61.901 1105.17 50.022 1138.76 50.102 1178.74 39.915 1235.36 39.678 1344.85 43.888 1434.82 66.912 1493.92 62.230 1614.97 60.669 1679.91 82.130 2932.88 86.038 3210.13 92.735 NMR

1H-NMR of tianeptine hemi-oxalate Form A (see FIG. 6) showed that the signals of the protons near the amine moiety were shifted downfield compared to the starting material. This suggests a possible interaction between the basic nitrogen and a carboxylic moiety of the coformer. Neither the presence of the coformer nor the stoichiometry of the sample could be confirmed by 1H-NMR analysis.

1H-NMR (400 MHz, dmso-d6) δ (ppm): 1.10-1.32 (m, 4H), 1.38-1.54 (m, 4H), 2.16 (t, J=7.5 Hz, 2H), 2.40-2.58 (br band, 2H+DMSO-d6), 3.37 (s, 3H), 5.34 (s, 1H), 7.33-7.60 (m, 4H), 7.76 (br s, 2H), 7.82 (br s, 1H).

Tianeptine hemi-oxalate Form A crystallizes as triclinic P-1 where a=9.5477(7)Å, b=11.4514(10)Å, c=11.8918(12)Å, α=113.071(9), β=94.351(7) ° and γ=100.164(7)°. The asymmetric unit is made of one protonated tianeptine molecule and half molecule of oxalate (see FIG. 7). The stoichiometry of the salt is 2:1 tianeptine to oxalate meaning the oxalate is a dianion.

The oxalate dianion forms hydrogen bonds with four different tianeptine molecules (see Table 12 and FIG. 8). The tianeptine carboxylic group interacts with the carboxylate group, while the amino group forms a bifurcated hydrogen bond with the two oxygen atoms of the oxalate as shown in FIG. 8.

TABLE 12 Hydrogen bond distances in tianeptine hemi-oxalate Donor-H • • • Acceptor Distance (Å) Intra N(1)—H(1B) . . . O(1) 2.762(3) O(3)—H(300) . . . O(7) 2.551(4) N(1)—H(1A) . . . O(7) 2.788(3) N(1)—H(1A) . . . O(6) 2.735(3)

TABLE 13 Atomic coordinates (×10⁴) and equivalent isotropic displacement parameters (Å2 × 10³) for tianeptine hemi-oxalate Form A x y Z U(eq) C(14) 1205(3) 6111(3) 3786(3) 41(1) C(1) 5009(3) 7193(3) 4985(3) 34(1) C(2) 5571(4) 7638(3) 6220(3) 45(1) C(3) 5203(4) 8732(3) 7060(3) 53(1) C(4) 4321(4) 9369(3) 6677(3) 51(1) C(5) 3757(3) 8902(3) 5434(3) 42(1) C(6) 4083(3) 7804(3) 4558(3) 33(1) C(7) 3349(3) 7316(3) 3232(3) 34(1) C(8) 4245(3) 7116(3) 2186(3) 34(1) C(9) 3644(4) 7303(3) 1189(3) 50(1) C(10) 4305(4) 7160(4)  164(3) 62(1) C(11) 5614(4) 6813(4)  118(3) 61(1) C(12) 6235(4) 6615(3) 1078(3) 51(1) C(13) 5578(3) 6764(3) 2120(3) 37(1) C(15)  −56(3) 4935(3) 3249(3) 41(1) C(16)  351(3) 3639(3) 2964(3) 45(1) C(17) −927(4) 2490(3) 2379(4) 60(1) C(18) −562(5) 1171(3) 2010(4) 73(1) C(19)  125(5)  944(3) 3033(4) 68(1) C(20)  477(4) −368(3) 2746(4) 57(1) C(21) 7782(4) 7559(4) 3692(4) 58(1) N(1) 2204(2) 6082(2) 2887(2) 36(1) N(2) 6413(3) 6588(2) 3078(2) 41(1) O(1) 4442(2) 4906(2) 3091(2) 42(1) O(2) 6693(3) 5568(2) 4545(2) 57(1) O(3) −238(3) −1283(2)  1694(3) 70(1) O(4) 1273(3) −557(3) 3438(3) 92(1) Cl(1) 5903(2) 9287(1) 8610(1) 98(1) S(1) 5633(1) 5905(1) 3894(1) 40(1) C(22) −288(3) 5635(3)  208(3) 34(1) O(6) −1158(2)  5753(2) −532(2) 52(1) O(7)  207(2) 6468(2) 1306(2) 43(1) U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.

TABLE 14 Bond lengths [Å] and angles [°] for tianeptine hemi-oxalate Form A C(14)—N(1) 1.480(4) C(14)—C(15) 1.519(4) C(1)—C(2) 1.379(4) C(1)—C(6) 1.399(4) C(1)—S(1) 1.773(3) C(2)—C(3) 1.386(5) C(3)—C(4) 1.366(5) C(3)—Cl(1) 1.730(3) C(4)—C(5) 1.385(5) C(5)—C(6) 1.386(4) C(6)—C(7) 1.514(4) C(7)—N(1) 1.514(3) C(7)—C(8) 1.529(4) C(8)—C(9) 1.386(4) C(8)—C(13) 1.400(4) C(9)—C(10) 1.381(5) C(10)—C(11) 1.375(5) C(11)—C(12) 1.361(5) C(12)—C(13) 1.396(4) C(13)—N(2) 1.440(4) C(15)—C(16) 1.516(4) C(16)—C(17) 1.514(4) C(17)—C(18) 1.511(5) C(18)—C(19) 1.471(5) C(19)—C(20) 1.511(5) C(20)—O(4) 1.184(4) C(20)—O(3) 1.311(4) C(21)—N(2) 1.478(4) N(2)—S(1) 1.615(3) O(1)—S(1) 1.426(2) O(2)—S(1) 1.423(2) C(22)—O(6) 1.227(3) C(22)—O(7) 1.269(3) C(22)—C(22)#1 1.555(6) N(1)—C(14)—C(15) 111.5(2) C(2)—C(1)—C(6) 122.4(3) C(2)—C(1)—S(1) 118.2(2) C(6)—C(1)—S(1) 119.1(2) C(1)—C(2)—C(3) 118.3(3) C(4)—C(3)—C(2) 121.1(3) C(4)—C(3)—C1(1) 120.6(3) C(2)—C(3)—C1(1) 118.3(3) C(3)—C(4)—C(5) 119.8(3) C(6)—C(5)—C(4) 121.4(3) C(5)—C(6)—C(1) 117.1(3) C(5)—C(6)—C(7) 117.8(3) C(1)—C(6)—C(7) 125.0(2) N(1)—C(7)—C(6) 110.6(2) N(1)—C(7)—C(8) 108.5(2) C(6)—C(7)—C(8) 120.3(2) C(9)—C(8)—C(13) 117.0(3) C(9)—C(8)—C(7) 115.1(3) C(13)—C(8)—C(7) 127.8(3) C(10)—C(9)—C(8) 122.8(3) C(11)—C(10)—C(9) 119.2(4) C(12)—C(11)—C(10) 119.7(4) C(11)—C(12)—C(13) 121.5(3) C(12)—C(13)—C(8) 119.8(3) C(12)—C(13)—N(2) 114.5(3) C(8)—C(13)—N(2) 125.7(3) C(16)—C(15)—C(14) 114.7(2) C(17)—C(16)—C(15) 112.9(3) C(18)—C(17)—C(16) 114.9(3) C(19)—C(18)—C(17) 115.1(3) C(18)—C(19)—C(20) 118.3(3) O(4)—C(20)—O(3) 123.6(3) O(4)—C(20)—C(19) 122.8(3) O(3)—C(20)—C(19) 113.5(3) C(14)—N(1)—C(7) 116.0(2) C(13)—N(2)—C(21) 116.4(3) C(13)—N(2)—S(1) 120.6(2) C(21)—N(2)—S(1) 116.4(2) O(2)—S(1)—O(1) 118.86(14) O(2)—S(1)—N(2) 108.81(14) O(1)—S(1)—N(2) 107.18(13) C(9)—C(8)—C(13) 117.0(3) C(9)—C(8)—C(7) 115.1(3) C(13)—C(8)—C(7) 127.8(3) C(10)—C(9)—C(8) 122.8(3) C(11)—C(10)—C(9) 119.2(4) C(12)—C(11)—C(10) 119.7(4) C(11)—C(12)—C(13) 121.5(3) C(12)—C(13)—C(8) 119.8(3) C(12)—C(13)—N(2) 114.5(3) C(8)—C(13)—N(2) 125.7(3) C(16)—C(15)—C(14) 114.7(2) C(17)—C(16)—C(15) 112.9(3) C(18)—C(17)—C(16) 114.9(3) C(19)—C(18)—C(17) 115.1(3) C(18)—C(19)—C(20) 118.3(3) O(4)—C(20)—O(3) 123.6(3) O(4)—C(20)—C(19) 122.8(3) O(3)—C(20)—C(19) 113.5(3) C(14)—N(1)—C(7) 116.0(2) C(13)—N(2)—C(21) 116.4(3) C(13)—N(2)—S(1) 120.6(2) C(21)—N(2)—S(1) 116.4(2) O(2)—S(1)—O(1) 118.86(14) O(2)—S(1)—N(2) 108.81(14) O(1)—S(1)—N(2) 107.18(13) C(13)—N(2)—S(1) 120.6(2) C(21)—N(2)—S(1) 116.4(2) O(2)—S(1)—O(1) 118.86(14) O(2)—S(1)—N(2) 108.81(14) O(1)—S(1)—N(2) 107.18(13) O(2)—S(1)—C(1) 108.21(14) O(1)—S(1)—C(1) 110.17(13) N(2)—S(1)—C(1) 102.35(14) O(6)—C(22)—O(7) 125.7(3) O(6)—C(22)—C(22)#1 118.6(3) O(7)—C(22)—C(22)#1 115.6(3) Solubility

The solubility of the tianeptine hemi-oxalate form A was compared with that of the tianeptine sodium salt at various pH using standard buffers as shown in Table 15 below.

TABLE 15 Solubility Comparison Prepared Tianeptine Hemi-Oxalate Tianeptine Sodium according Form A solubility solubility Medium to (mg/ml) (mg/ml) pH 1.2 USP 0.702 4.645 pH 4.5 USP 0.313 2.101 (Phosphate) pH 4.5 PhEu 0.317 3.676 (Acetate) pH 6.8 USP 0.585 1.768 (Phosphate) Water 20 mg in Soluble after 40 Freely Soluble 100 ml minutes of mixing with magnetic stirrer Hygroscopicity

The hygroscopicity of the tianeptine hemi-oxalate Form A was compared that of the tianeptine sodium salt. Crystals of the tianeptine samples were observed in open air or in closed conditions (crimped glass vial) under varying temperature and relative humidity (RH) parameters as shown in Tables 16-17 below. Hygroscopicity was measured as the percentage (%) of water in the sample using the Karl Fisher (KF) method at day 1, 3, and 7. While tianeptine sodium is extremely hygroscopic (Table 17), the water content of the tianeptine hemi-oxalate salt was practically unchanged after 7 days, in open air or in a crimped glass vial (Table 16).

TABLE 16 Hygroscopicity of Tianeptine hemi-oxalate Form A Time 1 day Time 3 days Time 7 days Tianeptine Storage Conditions Hemi- Crimped Crimped Crimped Oxalate Open glass Open glass Open glass Form A Time 0 Air vial Air vial Air vial 25° C., 0.47% 0.35% 0.34% 0.28% 0.18% 0.22% 0.28% 60% RH 30° C., 0.28% 0.27% 0.18% 0.16% 0.30% 0.30% 65% RH 40° C., 0.06% 0.30% 0.30% 0.16% 0.17% 0.20% 75% RH

TABLE 17 Hygroscopicity of Tianeptine Sodium Time 1 day Time 3 days Time 7 days Storage Conditions Crimped Crimped Crimped Tianeptine Open glass Open glass Open glass Sodium Time 0 Air vial Air vial Air vial 25° C., 3.09% 13.86% 2.94% NP 2.42% NP 2.56% 60% RH 30° C., 14.80% 2.63% NP 2.65% NP 2.77% 65% RH 40° C., 16.22% 2.84% NP 2.73% NP 2.53% 75% RH NP = Not performed due to visual decomposition of the extremely hygroscopic sample at day 1.

Example 2 Tianeptine Hemi-Oxalate and Mono-Oxalate Form a Mixture

The above reaction was repeated at a smaller scale to confirm the formation of the new species. 10-100 g of tianeptine free base was dissolved in 200-2000 mL of acetone and the solution was heated at reflux. 2-20 g (1 eq.) of oxalic acid were added to the clear solution and the resulting mixture was stirred at 40-60° C. for 30-60 minutes. The coformer was instantly solubilized and a clear solution was observed. After a few minutes, the formation of a white precipitate was observed. The mixture was then cooled at room temperature and stirred for 12-24 hours. The white precipitate was recovered under vacuum, washed with acetone and dried at 40-60° C. for 12-24 hours.

Replication of the reaction confirmed the presence of tianeptine mono-oxalate Form A in mixture with hemi-oxalate Form A. Such mixtures could also be obtained by mixing the two independently prepared species.

DSC analysis of the mixture showed two distinct endothermic peaks. The first endothermic peak at 176° C. (onset at 174.64° C.) and the second endothermic peak was detected at 200° C. (onset 195.45° C.), which was imputable to the melting and decomposition of the tianeptine hemi-oxalate Form A. TG analysis confirmed that the sample was dried and that the decomposition occurred below 17° C. in two distinct events where approximately 12% and 9% of weight was lost.

Melting point analysis of the mixture highlighted that the first event observed during the DSC analysis was ascribable to the melting of the sample without its decomposition (as visible at 166, 178 and 188° C.). The second endothermic event started with the melting of the sample followed by decomposition.

Interconversion Slurry Tests

The mixture was subjected to slurry experiments to evaluate potential conversion between the two salts. 100 mg was suspended in 2 mL of a single solvent and left under magnetic stirring at approximately 200 rpm at room temperature for 3 and 7 days as well as at 50° C. for 3 days. Afterwards, the samples were checked by XRPD analyses and the resulting diffractograms were compared to the XRPD patterns of the starting material and that of tianeptine hemi-oxalate Form A. The results of the slurry experiments are shown in Table 18.

TABLE 18 Results of the slurry experiments Solvent Slurry-3 days-RT Slurry-7 days-RT Slurry-50° C.-3 days Acetone tianeptine hemi- tianeptine hemi- tianeptine hemi- oxalate Form A + oxalate Form A + oxalate Form A tianeptine mono- tianeptine mono- oxalate Form A oxalate Form A Ethyl tianeptine hemi- tianeptine hemi- tianeptine hemi- Acetate oxalate Form A + oxalate Form A + oxalate Form A + tianeptine mono- tianeptine mono- tianeptine mono- oxalate Form A oxalate Form A oxalate Form A Stability of Tianeptine Hemi-Oxalate Salt

These analyses confirmed that tianeptine hemi-oxalate Form A is the most thermodynamically stable form due to its higher melting point and stability during slurry experiments. To assess the phase stability of the tianeptine hemi-oxalate Form A, several slurry experiments were performed in different solvents or solvent mixtures and different temperature conditions. No significant modifications in the XRPD pattern were observed after the tests. In addition, stability tests were carried out in different conditions of temperature (25-60° C.) and relative humidity (0-75% C). In all the tested conditions, the crystal form did not Grinding and water kneading experiments were conducted as well and they did not induce a phase shift. Based on the slurry experiments and stability tests performed Tianeptine hemi-oxalate Form A can be considered the thermodynamic stable form.

When the reaction ratio between tianeptine and oxalic acid was 2:1, the formation of tianeptine hemi-oxalate Form A was preferred, whereas when the ratio was 1:1 in some low polar solvents, the formation of tianeptine mono-oxalate Form A was favored.

Example 3 Tianeptine Mono-Oxalate Form A

The following synthetic methodology was used to prepare tianeptine mono-oxalate Form A. 2-20 g of tianeptine was dissolved in 200-2000 mL of ethyl acetate under magnetic stirring at 40-60° C. After 15-30 minutes, the hot clear solution was cooled to room temperature and left under stirring for 90-180 minutes, but the solution remained clear. 1-10 g of oxalic acid was dissolved in 20-200 mL of ethyl acetate at room temperature, obtaining a clear solution (concentration=50 mg/mL). 8-80 mL of the oxalic acid solution (1 eq.) was then added rapidly to the tianeptine solution under magnetic stirring at room temperature. A white powder instantly precipitated. After 60-90 minutes, the suspension was recovered under vacuum, washed with ethyl acetate, and dried under vacuum (10⁻² atm) at room temperature overnight.

The XRPD diffraction pattern and its peak list for tianeptine mono-oxalate Form A are illustrated in FIG. 10 and Table 19, respectively. The FT-IR spectrum for tianeptine mono-oxalate Form A is reported in FIG. 11 and its peak list is reported in Table 20.

TABLE 19 XRPD Peaks List of Tianeptine mono-Oxalate Form A Pos. Height FWHM d-spacing Rel. Int. [°2Th.] [cts] [°2Th.] [Å] [%] 5.7082 63.61 0.8029 15.48295 2.10 7.4941 709.24 0.1171 11.79669 23.46 8.2794 645.85 0.1171 10.67947 21.36 10.1224 3023.10 0.1338 8.73884 100.00 10.4738 2158.15 0.1338 8.44637 71.39 11.9311 1022.01 0.1171 7.41780 33.81 14.7375 1181.20 0.1171 6.01097 39.07 16.2068 732.25 0.0669 5.46918 24.22 16.3175 775.67 0.0836 5.43235 25.66 17.0803 441.14 0.1673 5.19140 14.59 17.9805 1507.42 0.1673 4.93348 49.86 18.1409 907.54 0.0836 4.89022 30.02 18.6654 1066.16 0.1506 4.75396 35.27 19.2422 130.86 0.1338 4.61275 4.33 19.8272 160.52 0.2007 4.47796 5.31 20.9993 2021.18 0.1840 4.23059 66.86 21.6871 986.74 0.1673 4.09795 32.64 22.0789 1127.40 0.2007 4.02611 37.29 22.7397 1599.50 0.0669 3.91058 52.91 22.9548 1145.78 0.1004 3.87441 37.90 23.3796 1431.11 0.1673 3.80498 47.34 23.9564 741.27 0.1428 3.71157 24.52 24.0542 767.99 0.0816 3.70589 25.40 24.9620 622.68 0.1224 3.56429 20.60 25.4332 493.19 0.0816 3.49931 16.31 25.8455 120.08 0.1224 3.44442 3.97 27.1812 272.70 0.1224 3.27811 9.02 28.2343 273.69 0.2856 3.15819 9.05 28.7192 564.65 0.1632 3.10596 18.68 29.8322 823.17 0.1428 2.99257 27.23 30.7901 374.48 0.1224 2.90161 12.39 31.8007 237.28 0.2856 2.81167 7.85 32.5020 239.28 0.1428 2.75258 7.91 33.7079 166.14 0.2040 2.65681 5.50 34.6256 49.87 0.2448 2.58847 1.65 35.1208 141.34 0.2448 2.55310 4.68 36.2371 158.16 0.2040 2.47697 5.23 36.5029 184.56 0.2448 2.45954 6.11 37.0868 179.15 0.3672 2.42215 5.93 38.2112 90.60 0.2448 2.35342 3.00 38.9995 95.43 0.4896 2.30765 3.16 39.7161 60.60 0.2448 2.26765 2.00

TABLE 20 FT-IR Peak List of Tianeptine mono-Oxalate Form A. Position (cm−1) Intensity [% T] 407 78.015 420 69.840 437 49.006 472 60.639 503 66.437 542 38.170 574 14.288 590 25.372 599 45.604 634 87.938 672 51.844 698 48.676 715 46.116 730 63.379 745 58.880 756 51.876 765 38.000 817 58.594 848 59.972 881 67.940 895 69.758 915 46.973 956 85.792 1012 82.832 1044 57.782 1058 61.391 1068 73.339 1103 53.620 1140 54.137 1162 39.190 1183 39.124 1206 58.980 1218 61.413 1241 35.677 1291 50.234 1319 66.721 1347 38.293 1393 55.381 1445 69.191 1459 74.454 1474 67.558 1500 73.813 1578 59.760 1623 44.368 1724 51.663 1763 57.945 2162 98.026 2324 93.872 2495 91.427 2633 89.069 2862 87.030 2932 84.185 3098 91.653 3177 86.700 3245 89.155

The DSC profile reported in FIG. 12 showed a sharp endothermic peak at 175° C. (onset 174.8° C.), which was associated with the melting of the sample. It also showed an exothermic peak at 179° C. associated to recrystallization of the sample. Two endothermic events were also observed at 196° C. These peaks were associated with the melting of tianeptine mono-oxalate Form A while the broad peak was due to the decomposition of the oxalic acid.

The TGA profile reported in FIG. 13 only showed the degradation of the sample during the thermal events seen in the DSC profile. The weight loss caused by the decomposition of the oxalic acid in CO₂ WAS 16.4%

Tianeptine mono-oxalate Form A was anhydrous, slightly hygroscopic and started to convert into tianeptine hemi-oxalate Form A at 40-60° C. under high humidity (75% RH) and by water kneading. It appeared stable if it was milled without water and if it was stored in milder conditions (25° C. and 60-75% RH) or at high temperatures (40-60° C.) without humidity (RH≈0%).

No significant difference in the water solubility at room temperature was visually observed between the two forms (lower than 1 mg/mL).

Example 4 Tianeptine Mono-Oxalate Form B

To prepare tianeptine mono-oxalate Form B, 50 mg of tianeptine free base was dissolved in 6.0 mL of nitromethane. 10 mg (1 equivalent) of oxalic acid was dissolved in 0.5 mL of nitromethane and the resulting solution was added to the solution of tianeptine. Immediately after the addition, the reaction mixture was cooled in an ice bath. After approximately 7 minutes, the white precipitate was recovered under vacuum and analyzed by XRPD.

The diffractogram and corresponding peak list of tianeptine mono-oxalate Form B are reported in FIG. 14 and Table 21. The FT-IR spectrum of tianeptine mono-oxalate Form B is reported in FIG. 15 and its peak list is reported in Table 22.

TABLE 21 XRPD Peaks List of Tianeptine mono-Oxalate Form B Pos. Height FWHM d-spacing Rel. Int. [°2Th.] [cts] [°2Th.] [Å] [%] 5.9877 53.99 0.2007 14.76081 2.46 7.4484 644.86 0.1171 11.86894 29.42 7.8000 332.97 0.1171 11.33473 15.19 8.6132 2191.71 0.1506 10.26635 100.00 10.4137 1467.04 0.1338 8.49500 66.94 10.7756 561.19 0.1171 8.21054 25.61 12.0662 111.82 0.1338 7.33509 5.10 13.6920 257.13 0.0836 6.46751 11.73 14.8560 875.54 0.1840 5.96332 39.95 15.5731 811.65 0.1338 5.69028 37.03 16.0391 451.42 0.1506 5.52600 20.60 17.4715 795.13 0.1338 5.07603 36.28 17.8589 167.53 0.1338 4.96679 7.64 18.8422 163.02 0.1004 4.70975 7.44 19.2387 206.33 0.1338 4.61359 9.41 19.8786 562.24 0.1338 4.46648 25.65 20.2416 478.57 0.1004 4.38719 21.84 20.4483 579.19 0.1338 4.34331 26.43 20.9058 684.79 0.1171 4.24929 31.24 21.2650 622.71 0.1338 4.17831 28.41 21.6364 453.54 0.1338 4.10743 20.69 21.9569 437.70 0.1171 4.04820 19.97 22.7958 225.10 0.0669 3.90109 10.27 23.4708 1586.21 0.1506 3.79039 72.37 23.7824 397.64 0.1338 3.74144 18.14 24.3598 833.23 0.1506 3.65404 38.02 24.6971 1117.13 0.1506 3.60489 50.97 25.2005 227.05 0.1506 3.53402 10.36 25.7272 95.62 0.1338 3.46284 4.36 26.7623 64.66 0.1673 3.33121 2.95 27.3979 469.15 0.1171 3.25537 21.41 27.6142 248.09 0.1004 3.23036 11.32 29.0818 182.64 0.1004 3.07059 8.33 29.5176 62.93 0.1004 3.02624 2.87 30.1255 254.64 0.1506 2.96655 11.62 30.4403 205.52 0.1004 2.93658 9.38 30.8331 56.14 0.1338 2.90006 2.56 31.3986 69.24 0.1338 2.84911 3.16 31.7911 85.16 0.2007 2.81483 3.89 32.3064 438.17 0.1224 2.76880 19.99 32.4065 443.19 0.0816 2.76733 20.22 33.1884 54.59 0.1632 2.69721 2.49 33.8013 48.48 0.1632 2.64969 2.21 34.5438 170.40 0.1020 2.59441 7.77 35.4188 36.28 0.2448 2.53230 1.66 35.8785 69.62 0.1224 2.50091 3.18 36.2912 126.50 0.2040 2.47341 5.77 37.2195 37.44 0.2448 2.41382 1.71 38.2239 25.23 0.2856 2.35267 1.15 39.0687 83.00 0.2040 2.30372 3.79

TABLE 22 FT-IR Peak List of Tianeptine mono-Oxalate Form B Position (cm−1) Intensity [% T] 417 80.583 433 60.709 470 61.112 490 73.589 506 74.658 542 44.891 573 33.138 588 34.548 598 45.975 636 88.682 672 64.770 697 62.702 718 53.966 726 58.476 743 69.288 754 66.477 767 56.363 806 74.846 817 74.210 842 71.115 858 71.329 892 75.547 913 60.377 1009 87.441 1043 64.997 1053 74.675 1066 76.779 1107 63.129 1140 60.337 1181 44.309 1217 50.155 1240 43.325 1289 69.256 1355 58.928 1407 72.611 1445 80.501 1474 80.926 1495 79.647 1575 71.109 1618 58.270 1716 60.858 1755 70.768 2324 96.331 2859 88.179 2932 85.760 3178 90.209

The DSC profile (FIG. 16) shows a sharp endothermic peak at 178° C. (onset 177.3° C.), which was associated with the sample melting. It also showed two endothermic events that took place at 197° C. These events were probably associated with the melting of tianeptine mono-oxalate while the broad peak was due to the decomposition of the oxalic acid.

While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.

The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and devices within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods or devices, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict any definitions in this disclosure. 

What is claimed is:
 1. An anhydrous crystalline hemi-oxalate salt of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f] [1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide (tianeptine), wherein the salt exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak selected from the group consisting of 8.2, 8.6, 9.1, and 9.5 degrees 2θ±0.3 degrees 2θ.
 2. The compound of claim 1, wherein the tianeptine hemi-oxalate salt exhibits an XRPD pattern comprising at least one additional peak selected from the group consisting of 4.5, 11.5, 14.2, 15.2, 15.8, 16.4, 19.2, 22.1, 23.9, 26.9, and 27.4 degrees 2θ±0.3 degrees 2θ.
 3. An anhydrous crystalline tianeptine mono-oxalate salt of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f] [1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide (tianeptine), wherein the salt exhibits an X-ray diffraction pattern (XRPD) comprising at least one peak selected from the group consisting of 10.1 and 10.5 degrees 2θ±0.3 degrees 2θ.
 4. The compound of claim 3, wherein the crystalline tianeptine mono-oxalate salt exhibits an XRPD pattern comprising at least one additional peak selected from the group consisting of 7.5, 8.3, 11.9, 14.7, 16.2, 16.3, 17.9, 18.7, 21.0, 21.7, and 22.1 degrees 2θ±0.3 degrees 2θ.
 5. A mixture of an anhydrous hemi-oxalate salt and an anhydrous crystalline mono-oxalate salt of (RS)-7-(3-chloro-6-methyl-6,11-dihydrodibenzo[c,f] [1,2]thiazepin-11-ylamino)heptanoic acid S,S-dioxide (tianeptine), wherein the mixture exhibits an XRPD pattern comprising at least one peak selected from the group consisting of 10.1 and 10.5 degrees 2θ±0.3 degrees 2θ.
 6. The mixture of claim 5, wherein the mixture exhibits an XRPD pattern further comprising at least one additional peak selected from the group consisting of 7.5, 8.3, 11.9, 14.7, 16.2, 16.3, 17.9, 18.7, 21.0, 21.7, and 22.1 degrees 2θ±0.3 degrees 2θ. 